The IEEE (Institute of Electrical and Electronics Engineers) 802.16 standards propose using an Orthogonal Frequency Division Multiple Access (OFDMA) for transmission of data over an air interface. OFDMA has also been proposed for use in 3GPP (Third Generation Partnership Project) Evolution communication systems. In an OFDMA communication system, a frequency bandwidth is split into multiple contiguous frequency sub-bands, or subcarriers, that are transmitted simultaneously. A user may then be assigned one or more of the frequency sub-bands for an exchange of user information, thereby permitting multiple users to transmit simultaneously on the different sub-carriers. These sub-carriers are orthogonal to each other, and thus intra-cell interference is minimized.
In order to maximize bandwidth usage, OFDMA communication systems engage in frequency selective scheduling. That is, for any given Transmission Time Interval (TTI), the sub-bands may be allocated to users based on measured channel conditions. Further, an appropriate modulation scheme and coding scheme may be determined for each sub-band and each TTI based on the measured channel conditions. The channel condition measurements are performed by a user equipment (UE), which UE measures channel conditions for each and every sub-band during a measuring period, such as a Transmission Time Interval (TTI) (also known as a sub-frame) or a radio frame transmission period, and then reports the measured channel conditions for all of the sub-bands to a serving Node B in a Channel Quality Information (CQI) message. Based on the reported CQIs, an OFDMA communication system is able to determine a fading profile of a frequency bandwidth and selectively schedule the sub-bands over a scheduling period, typically one or more TTIs or radio frames, and further adaptively determine appropriate modulation and coding schemes for each sub-band during the scheduling period. However, reporting a CQI for each and every sub-band may consume a significant amount of uplink system overhead, especially for OFDMA systems utilizing a 20 megahertz (MHz) bandwidth and employing as many as 100 sub-bands within that bandwidth.
Therefore, a need exists for a method and apparatus that provides channel quality information sufficient to construct a fading profile of a frequency bandwidth and that does not consuming the overhead resulting from the reporting of CQI for every sub-band of the frequency bandwidth.